zephyr/drivers: it8xxx2: flash protection API is deprecated
zephyr/drivers: it8xxx2: flash protection API is deprecated

The function of flash_write_protection_set() is deprecated and will
be removed in Zephyr 2.8.

BUG=b:187192628
BRANCH=none
TEST=No warning while building the board of hayato on zephyr2.6

Change-Id: I65e38557d7d65b6f079f20af7ecc098e30d57220
Signed-off-by: Tim Lin <38846f7070d5770410e9ef8b439c72e7b53a72c5@ite.corp-partner.google.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3023747
Reviewed-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Reviewed-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Tested-by: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>
Commit-Queue: Denis Brockus <6b21e8190fb5e373363fb95271367073a16474ef@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec